The invention relates to rupture discs and, more particularly, to a quick-release assembly for a rupture disc insert type holder and the like, such as a graphite rupture disc, an orifice plate, and other piping accessories which fit inside bolted pipe flanges.
A rupture disc is well known in the art, being an engineered weak spot in a pressurized system which will rupture at a predetermined pressure and temperature. In modern processing equipment utilizing increasingly higher pressures and temperatures and faster speeds, there are three unpredictable conditions which can result in an unforeseen pressure rise causing an explosion with disastrous results, these conditions being power failure, air failure and human error. It is, therefore, required for all pressurized systems to be protected by a pressure relieving device to prevent the pressure from rising a predetermined percentage above the maximum workable working pressure of the system.
The above problem is easily handled by a rupture disc which is the ultimate in simplicity in that it has no moving parts, depending solely on the known strength of a thin metal diaphragm to function. The rupture disc has been proved to be more reliable than a relief valve, in that a relief valve has moving parts and precision machined surfaces which must interact perfectly, where the machining, assembly and setting of relief valves are all subject to human error. The complete rupture disc assembly, which includes the rupture disc and disc holder, is known as a safety head.
Rupture discs are normally disposed within holders, the holder being a two piece unit including a base flange disposed on the inlet side and a holddown flange disposed on the outlet side. The inner faces of these flanges grip the rupture disc therebetween in a sandwich arrangement to form a leak-tight seal. Insert type holders are disposed between companion pipe flanges which are bolted together. However, these pipe flanges require a great number of bolts secured around the insert type holder, which creates a time consuming and costly problem when the rupture disc within the insert type holder needs to be replaced or inspected. Accordingly, all of the bolts must be loosened, there usually being eight bolts or more, and at least half of the bolts must be removed. The pipe flanges usually must be forced apart by two men using pry bars before the insert type holder containing the rupture disc can be removed from between the pipe flanges.
U.S. Pat. Nos. 4,444,214 and 4,505,289 disclose rupture disc apparatus which eliminates the necessity of loosening or removing any bolts in order to insert or remove the rupture disc therefrom, as required above with the prior art companion pipe flanges. The rupture disc apparatus of these patents includes a fixed receptacle for receiving a cartridge having a rupture disc mounted therein. The fixed receptacle is mounted in a pressure relief vent to communicate on opposite sides thereof with the vent. The receptacle includes seating rings which are spring biased for seating on opposite sides of the cartridge. The rupture disc holding cartridge can only be inserted into the receptacle or removed therefrom when the vent pressure therein is substantially at atmospheric pressure. Accordingly, the rings are urged into locking position when the vent pressure is increased above atmospheric pressure, whereby the rings will not permit the cartridge to be removed from the receptacle until the vent pressure is again decreased to atmospheric pressure. It is understood, that the seating rings and their associated springs must be precisioned machine so that they interact perfectly during the movement of these parts, without being subject to human error.